Engineering of inorg.-​org. lead halide perovskites for photovoltaic applications has experienced significant advances in recent years. However, the use of the relatively expensive spiro-​OMeTAD as a hole-​transporting material (HTM) poses a challenge due to dopant-​induced degrdn. Herein we introduce two new three-​armed and four-​armed HTMs (BTT-​4 and BTT-​5) based on isomeric forms of benzotrithiophene (BTT)​. The isomerism impact on the optical, electrochem. and photophys. properties and the photovoltaic performance is systematically investigated. Perovskite solar cells (PSCs) using BTT-​4 and BTT-​5 as HTMs show remarkable light-​to-​energy conversion efficiencies of 19.0​% and 18.2​%, resp., under std. measurement conditions. These results validate the readily available BTT heteroarom. structure as a valuable core for the design of highly efficient HTMs for the prepn. of PSCs.